In a spark ignition system an igniter, such as for instance a spark plug, is used to ignite an air-fuel mixture within a combustion zone. It is desirable to dilute the combustible mixture by increasing the air/fuel ratio, or by increasing the level of exhaust gas recirculation (EGR), which enables operation at higher compression ratios and loads and achieves cleaner and more efficient combustion. Unfortunately, operation at these increased dilution levels gives rise to problems relating to both ignition and flame propagation, necessitating the use of a robust ignition source to ensure successful ignition and stable combustion.
Additional problems are encountered in engines that have a stratified in-cylinder charge and strong charge motion. Under such conditions a long sparking duration is used so as to increase the probability of catching the optimum mixture pocket near the igniter, thereby improving ignition reliability. It has been reported that a longer duration spark with low peak current has better ignition properties than a shorter duration spark with higher peak current under the enhanced charge motion condition.
It would be beneficial to provide a spark ignition system and related methods that achieve reliable combustion results at lean and/or EGR cylinder charges below the limits that are currently encountered.